1. Field of the Invention
The present invention relates to an image signal format detection apparatus and method, and more particularly, to an image signal format detection apparatus and method capable of detecting images converted from progressive format images to interlace format images by an application of a 2:2 pull-down algorithm.
2. Description of the Related Art
In general, an image display device employs either an interlace scan mode or a progressive scan mode. The interlace scan mode is used for general TVs and the like, and includes a division of one image frame into two fields and a display of the fields on a screen one after the other, in order, when displaying one image. At this time, the two fields are referred to as a top field and bottom field, an upper field and lower field, an odd field or even field, and so on. On the other hand, the progressive scan or non-interlace scan mode is used for computer monitors, digital TVs, and so on, and includes a display of an entire frame image, all at once, by dealing with one image frame, as a frame unit, e.g., film being displayed on a screen.
For example, in case of 480-line National Television System Committee (NTSC) interlace scan mode (precisely, 487 valid lines in 525 lines), one frame is divided into two 240-line fields for display, and the divided 240-line fields, as noted above, are displayed on a screen one after the other every 1/60 seconds (480/60 i). On the other hand, the progressive scan mode completely displays the entire frame image, e.g., a 480-line image, all at once every 1/60 seconds (480/60 p). Accordingly, a progressive format image based on the progressive scan mode has a better image quality compared to an interlace format image.
One of the typical video formats that is closely related to such a progressive scan mode is a DVD movie formatted for display on an analog television and initially produced on film, since the original sources for almost all DVD movie titles released in recent years are produced on film first. Movies are produced at 24 frames per second, differently from NTSC TV programs. In the case of a DVD movie, it is, of course, possible to directly manufacture a DVD including the original images of 24 frames, as in an original film movie. However, since a majority of image display devices, such as general analog televisions, at present adopt the interlace scan mode, it is more practical to produce DVD movie titles in the interlace scan mode.
Accordingly, a process is required for converting a 24-frame progressive film into 60-field interlace images, which is typically referred to as a 3:2 pull-down or a “telecine.” The 3:2 pull-down process is a process that converts two 24 Hz frames into five 60 Hz fields, producing three fields repeatedly from the first frame and two fields from the second frame.
Meanwhile, 30-frame-per-second progressive format images are typically used for advertisement broadcasts, music videos, or the like, for which a 2:2 pull-down, similar to the 3:2 pull-down, is used. That is, the 2:2 pull-down refers to a process for converting 30-frame progressive format film into 60-field interlace format images.
FIG. 1 illustrates the 2:2 pull-down. In FIG. 1, images produced in the 30-frame-per-second progressive format are converted into the 60 Hz interlace format by dividing each frame into two fields. For example, a Frame 1 is converted into two fields T1 and B1, and a Frame 2 into two fields T2 and B2, and so on.
However, as it has become more necessary to exchange data among devices using different scan modes as the use of image display devices employing the progressive scan mode increases, an interlaced-to-progressive conversion (IPC) method becomes necessary to convert the interlace scan mode into the progressive scan mode. During such an IPC process, if it is known that a currently input image is a 2:2 pull-down-converted image, a complete progressive format image before the 2:2 pull-down can be easily obtained merely by combining interlace format fields. Accordingly, before implementing the IPC method, it becomes necessary to detect whether a field to be interpolated is for a previously 2:2 pull-down converted image.
Conventional systems mainly use the 3:2 pull-down, and conventional technologies have been disclosed, especially, in U.S. Pat. No. 5,398,071 entitled “Film To Video Format Detection For Digital Television” for methods for detecting such 3:2 pull-down format images. However, few or no technologies have been known to detect 2:2 pull-down format images through a relatively simple structure. Therefore, an image signal format detection apparatus and method is desired to detect the 2:2 pull-down format through a relatively simple structure.